1. Field of the Invention
The present invention relates to a positioning apparatus and particularly relates to a positioning apparatus mounted with vibration isolators and a robot.
2. Description of the Related Art
In such a positioning apparatus as a machine tool and a measurement apparatus, floor vibrations at an installation site may influence machining, measured results, or the like. In a machine tool, a measurement apparatus, or the like that requires particularly precision position control, it is common to provide a structure that does not propagate the floor vibrations, by mounting of vibration isolators. It is difficult for simple vibration isolators with use of anti-vibration rubber to isolate vibrations with low frequency (50 Hz or lower), and thus an air damper that causes suspension with use of pneumatic pressure, a magnet damper that causes suspension with use of magnetic force, or the like is used in a vibration isolator with high accuracy. Japanese Patent Application Laid-Open No. 2007-155038 discloses a vibration control device in which air actuators and sensors are unitized.
FIGS. 11 and 12 illustrate configurations of prior art techniques. In FIG. 11, a robot requires a long distance for attachment and detachment of a work, because the robot is installed on a floor, and thus a large robot 90 is required as the robot. In order to prevent deviation in relative position with respect to the large robot 90 for automation of work replacement by the robot, a lathe 91 is mounted with no vibration isolators and a base 92 integrated with leg parts is used with the lathe 91. In absence of the vibration isolators, precision machining cannot be carried out due to reception of influence of the floor vibrations.
In FIG. 12, vibration isolators 10 for a precision lathe 1 isolate the floor vibrations while always keeping a suspended state. Relative position between the large robot 90 which is installed on a floor and which carries out attachment and detachment of a work and a vacuum chuck face to which the work is to be attached undergoes deviation that is caused by the vibration isolators. In order to correct amount of the deviation, an image is captured by a CCD camera 93, mounted on the robot, before attachment of the work and the amount of the deviation in the position is calculated by comparison with a reference image stored in a controller for the robot and is fed back for position of the robot. It is thus necessary to separately mount sensors such as the CCD camera 93 and to provide a device and software that feed back information from the sensors for correction of the position of the robot.
In general, vibration isolators are intended for isolating floor vibrations and are not required to keep strictly the same posture. Accordingly, a machine tool or a measurement apparatus does not always have the same posture and position when viewed from a floor as a static system. In case where the posture of the machine tool or the measurement apparatus, that is, an inclination of the machine tool or the measurement apparatus is changed in some degree, the machine tool or the measurement apparatus itself receives no influence in accuracy, as long as sufficient machine rigidity is provided, and there is no problem in use of the machine tool or the measurement apparatus alone.
Considering use in combination with a robot for automation, on the other hand, coordinates on the machine as viewed from the robot fixed to the floor deviate due to intervention of the vibration isolators.
Therefore, the positional deviation is required to be corrected on condition that the robot carries out attachment and detachment of a tool or a work on the machine.
Correction of the positional deviation can be carried out by correction of hand position of the robot with mounting of separate sensors such as camera and measurement of the amount of the positional deviation. This method, however, requires the separate sensors and a device or software that feeds back the amount of the deviation to the robot.
As another solution, the influence of the positional deviation caused by the vibration isolators can be cancelled by mounting of the robot on the machine, that is, above the vibration isolators. This solution obviates necessity of addition of devices such as the sensors. The mounting on the machine shortens distance from the robot to the tool or the work, thus allows employment of the robot having a smaller size, and contributes to reduction in installation area and costs.
On condition that the robot fixed to the floor is operated at high speed, reactions thereto are exerted only onto the floor and thus little or no influence is exercised on the accuracy of the machine tool or the measurement apparatus. On condition that the robot is mounted on the machine as described above, by contrast, the reactions to high-speed operation of the robot are directly conveyed to the machine tool or the measurement apparatus. In particular, the machine tool or the measurement apparatus that has high precision is suspended through agency of the vibration isolators and is thus shaken greatly when subjected to a strong reaction. Great disturbance is not assumed for the machine tool and the measurement apparatus that have high precision and thus great shaking of the machine tool or the measurement apparatus makes it impossible to hold a position thereof by servo motors and triggers an alarm.